1. Field of the Invention
The present invention relates to a webbing tension device adapted for use in a seatbelt system for protecting an occupant in an emergency situation of a vehicle and more particularly to a webbing tension device imparting a tension to an occupant restraining webbing to closely restrain the occupant with the webbing in the emergency situation of the vehicle.
2. Description of the Prior Art
The seatbelt system is so constructed that the webbing, one end portion thereof being retracted in layers into a webbing retractor, is applied to the occupant and he is closely restrained by the webbing in an emergency situation of the vehicle.
The webbing retractor retracting the webbing therein imparts a predetermined tension to the webbing, but as a retracting force of the webbing retractor is made relatively weak or it is completely removed so as not to give the occupant a sense of oppression, a clearance is formed between the occupant and the webbing restraining the occupant, i.e., the webbing restraining the occupant has a slack. Accordingly, it is thought that in the emergency situation of the vehicle the occupant is moved in a direction of such an accident as a collision by the clearance amount until the occupant is surely restrained by the webbing after an unwinding of the webbing is stopped.
For this reason, a webbing tension device transmitting a biasing force of such resilient means as a spiral spring to a webbing takeup shaft of the webbing retractor, thereby imparting a tension to the webbing in the emergency situation of the vehicle has been proposed in a prior art. In such a device the takeup shaft is biased in a direction of a webbing retraction only by a biasing force of small resilient means in an ordinary running situation of the vehicle, but in the emergency situation of the vehicle a biasing force of large resilient means is transmitted to the takeup shaft, thereby retracting the webbing on the takeup shaft forcibly. However, the biasing force of the large resilient means acting upon the takeup shaft in the emergency situation continues to act thereupon, even after the vehicle is released from the emergency situation, which results in difficulty of operations in release of the webbing from its restraining situation on the occupant and in reuse of the seatbelt system.